Golang context.Context类代码示例

func (cq *ChanQueue) process(ctx context.Context) {
	// construct the channels here to be able to use them bidirectionally
	enqChan := make(chan peer.ID)
	deqChan := make(chan peer.ID)

	cq.EnqChan = enqChan
	cq.DeqChan = deqChan

	go func() {
		log.Debug("processing")
		defer log.Debug("closed")
		defer close(deqChan)

		var next peer.ID
		var item peer.ID
		var more bool

		for {
			if cq.Queue.Len() == 0 {
				// log.Debug("wait for enqueue")
				select {
				case next, more = <-enqChan:
					if !more {
						return
					}
					// log.Debug("got", next)

				case <-ctx.Done():
					return
				}

			} else {
				next = cq.Queue.Dequeue()
				// log.Debug("peek", next)
			}

			select {
			case item, more = <-enqChan:
				if !more {
					if cq.Queue.Len() > 0 {
						return // we're done done.
					}
					enqChan = nil // closed, so no use.
				}
				// log.Debug("got", item)
				cq.Queue.Enqueue(item)
				cq.Queue.Enqueue(next) // order may have changed.
				next = ""

			case deqChan <- next:
				// log.Debug("dequeued", next)
				next = ""

			case <-ctx.Done():
				return
			}
		}

	}()
}

// Do sends an HTTP request with the provided http.Client and returns an HTTP response.
// If the client is nil, http.DefaultClient is used.
// If the context is canceled or times out, ctx.Err() will be returned.
func Do(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
	if client == nil {
		client = http.DefaultClient
	}

	// Request cancelation changed in Go 1.5, see cancelreq.go and cancelreq_go14.go.
	cancel := canceler(client, req)

	type responseAndError struct {
		resp *http.Response
		err  error
	}
	result := make(chan responseAndError, 1)

	go func() {
		resp, err := client.Do(req)
		result <- responseAndError{resp, err}
	}()

	select {
	case <-ctx.Done():
		cancel()
		return nil, ctx.Err()
	case r := <-result:
		return r.resp, r.err
	}
}

func (ps *PingService) Ping(ctx context.Context, p peer.ID) (<-chan time.Duration, error) {
	s, err := ps.Host.NewStream(ID, p)
	if err != nil {
		return nil, err
	}

	out := make(chan time.Duration)
	go func() {
		defer close(out)
		for {
			select {
			case <-ctx.Done():
				return
			default:
				t, err := ping(s)
				if err != nil {
					log.Debugf("ping error: %s", err)
					return
				}

				select {
				case out <- t:
				case <-ctx.Done():
					return
				}
			}
		}
	}()

	return out, nil
}

func MetadataFromContext(ctx context.Context) (Metadata, error) {
	value := ctx.Value(metadataKey)
	if value != nil {
		metadata, ok := value.(Metadata)
		if ok {
			return metadata, nil
		}
	}
	return nil, errors.New("context contains no metadata")
}

// CloseAfterContext schedules the process to close after the given
// context is done. It is the equivalent of:
//
//   func CloseAfterContext(p goprocess.Process, ctx context.Context) {
//     go func() {
//       <-ctx.Done()
//       p.Close()
//     }()
//   }
//
func CloseAfterContext(p goprocess.Process, ctx context.Context) {
	if p == nil {
		panic("nil Process")
	}
	if ctx == nil {
		panic("nil Context")
	}

	// context.Background(). if ctx.Done() is nil, it will never be done.
	// we check for this to avoid wasting a goroutine forever.
	if ctx.Done() == nil {
		return
	}

	go func() {
		<-ctx.Done()
		p.Close()
	}()
}

func readMsgCtx(ctx context.Context, r msgio.Reader, p proto.Message) ([]byte, error) {
	var msg []byte

	// read in a goroutine so we can exit when our context is cancelled.
	done := make(chan error)
	go func() {
		var err error
		msg, err = r.ReadMsg()
		select {
		case done <- err:
		case <-ctx.Done():
		}
	}()

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case e := <-done:
		if e != nil {
			return nil, e
		}
	}

	return msg, proto.Unmarshal(msg, p)
}

func echoListen(ctx context.Context, listener Listener) {
	for {
		c, err := listener.Accept()
		if err != nil {

			select {
			case <-ctx.Done():
				return
			default:
			}

			if ne, ok := err.(net.Error); ok && ne.Temporary() {
				<-time.After(time.Microsecond * 10)
				continue
			}

			log.Debugf("echoListen: listener appears to be closing")
			return
		}

		go echo(c.(Conn))
	}
}

// dialPeer opens a connection to peer, and makes sure to identify
// the connection once it has been opened.
func (h *BasicHost) dialPeer(ctx context.Context, p peer.ID) error {
	log.Debugf("host %s dialing %s", h.ID, p)
	c, err := h.Network().DialPeer(ctx, p)
	if err != nil {
		return err
	}

	// identify the connection before returning.
	done := make(chan struct{})
	go func() {
		h.ids.IdentifyConn(c)
		close(done)
	}()

	// respect don contexteone
	select {
	case <-done:
	case <-ctx.Done():
		return ctx.Err()
	}

	log.Debugf("host %s finished dialing %s", h.ID, p)
	return nil
}

// writeMsgCtx is used by the
func writeMsgCtx(ctx context.Context, w msgio.Writer, msg proto.Message) ([]byte, error) {
	enc, err := proto.Marshal(msg)
	if err != nil {
		return nil, err
	}

	// write in a goroutine so we can exit when our context is cancelled.
	done := make(chan error)
	go func(m []byte) {
		err := w.WriteMsg(m)
		select {
		case done <- err:
		case <-ctx.Done():
		}
	}(enc)

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case e := <-done:
		return enc, e
	}
}

func (s *Swarm) dialAddrs(ctx context.Context, p peer.ID, remoteAddrs []ma.Multiaddr) (conn.Conn, error) {

	// sort addresses so preferred addresses are dialed sooner
	sort.Sort(AddrList(remoteAddrs))

	// try to connect to one of the peer's known addresses.
	// we dial concurrently to each of the addresses, which:
	// * makes the process faster overall
	// * attempts to get the fastest connection available.
	// * mitigates the waste of trying bad addresses
	log.Debugf("%s swarm dialing %s %s", s.local, p, remoteAddrs)

	ctx, cancel := context.WithCancel(ctx)
	defer cancel() // cancel work when we exit func

	conns := make(chan conn.Conn)
	errs := make(chan error, len(remoteAddrs))

	// dialSingleAddr is used in the rate-limited async thing below.
	dialSingleAddr := func(addr ma.Multiaddr) {
		// rebind chans in scope so we can nil them out easily
		connsout := conns
		errsout := errs

		connC, err := s.dialAddr(ctx, p, addr)
		if err != nil {
			connsout = nil
		} else if connC == nil {
			// NOTE: this really should never happen
			log.Errorf("failed to dial %s %s and got no error!", p, addr)
			err = fmt.Errorf("failed to dial %s %s", p, addr)
			connsout = nil
		} else {
			errsout = nil
		}

		// check parent still wants our results
		select {
		case <-ctx.Done():
			if connC != nil {
				connC.Close()
			}
		case errsout <- err:
		case connsout <- connC:
		}
	}

	// this whole thing is in a goroutine so we can use foundConn
	// to end early.
	go func() {
		limiter := make(chan struct{}, 8)
		for _, addr := range remoteAddrs {
			// returns whatever ratelimiting is acceptable for workerAddr.
			// may not rate limit at all.
			rl := s.addrDialRateLimit(addr)
			select {
			case <-ctx.Done(): // our context was cancelled
				return
			case rl <- struct{}{}:
				// take the token, move on
			}

			select {
			case <-ctx.Done(): // our context was cancelled
				return
			case limiter <- struct{}{}:
				// take the token, move on
			}

			go func(rlc <-chan struct{}, a ma.Multiaddr) {
				dialSingleAddr(a)
				<-limiter
				<-rlc
			}(rl, addr)
		}
	}()

	// wair for the results.
	exitErr := fmt.Errorf("failed to dial %s", p)
	for range remoteAddrs {
		select {
		case exitErr = <-errs: //
			log.Debug("dial error: ", exitErr)
		case connC := <-conns:
			// take the first + return asap
			return connC, nil
		case <-ctx.Done():
			// break out and return error
			break
		}
	}
	return nil, exitErr
}

// gatedDialAttempt is an attempt to dial a node. It is gated by the swarm's
// dial synchronization systems: dialsync and dialbackoff.
func (s *Swarm) gatedDialAttempt(ctx context.Context, p peer.ID) (*Conn, error) {
	var logdial = lgbl.Dial("swarm", s.LocalPeer(), p, nil, nil)
	defer log.EventBegin(ctx, "swarmDialAttemptSync", logdial).Done()

	// check if we already have an open connection first
	conn := s.bestConnectionToPeer(p)
	if conn != nil {
		return conn, nil
	}

	// check if there's an ongoing dial to this peer
	if ok, wait := s.dsync.Lock(p); ok {
		defer s.dsync.Unlock(p)

		// if this peer has been backed off, lets get out of here
		if s.backf.Backoff(p) {
			log.Event(ctx, "swarmDialBackoff", logdial)
			return nil, ErrDialBackoff
		}

		// ok, we have been charged to dial! let's do it.
		// if it succeeds, dial will add the conn to the swarm itself.
		defer log.EventBegin(ctx, "swarmDialAttemptStart", logdial).Done()
		ctxT, cancel := context.WithTimeout(ctx, s.dialT)
		conn, err := s.dial(ctxT, p)
		cancel()
		log.Debugf("dial end %s", conn)
		if err != nil {
			log.Event(ctx, "swarmDialBackoffAdd", logdial)
			s.backf.AddBackoff(p) // let others know to backoff

			// ok, we failed. try again. (if loop is done, our error is output)
			return nil, fmt.Errorf("dial attempt failed: %s", err)
		}
		log.Event(ctx, "swarmDialBackoffClear", logdial)
		s.backf.Clear(p) // okay, no longer need to backoff
		return conn, nil

	} else {
		// we did not dial. we must wait for someone else to dial.

		// check whether we should backoff first...
		if s.backf.Backoff(p) {
			log.Event(ctx, "swarmDialBackoff", logdial)
			return nil, ErrDialBackoff
		}

		defer log.EventBegin(ctx, "swarmDialWait", logdial).Done()
		select {
		case <-wait: // wait for that other dial to finish.

			// see if it worked, OR we got an incoming dial in the meantime...
			conn := s.bestConnectionToPeer(p)
			if conn != nil {
				return conn, nil
			}
			return nil, ErrDialFailed
		case <-ctx.Done(): // or we may have to bail...
			return nil, ctx.Err()
		}
	}
}

// Dial connects to a peer over a particular address
// Ensures raddr is part of peer.Addresses()
// Example: d.DialAddr(ctx, peer.Addresses()[0], peer)
func (d *Dialer) Dial(ctx context.Context, raddr ma.Multiaddr, remote peer.ID) (Conn, error) {
	logdial := lgbl.Dial("conn", d.LocalPeer, remote, nil, raddr)
	logdial["encrypted"] = (d.PrivateKey != nil) // log wether this will be an encrypted dial or not.
	defer log.EventBegin(ctx, "connDial", logdial).Done()

	var connOut Conn
	var errOut error
	done := make(chan struct{})

	// do it async to ensure we respect don contexteone
	go func() {
		defer func() {
			select {
			case done <- struct{}{}:
			case <-ctx.Done():
			}
		}()

		maconn, err := d.rawConnDial(ctx, raddr, remote)
		if err != nil {
			errOut = err
			return
		}

		if d.Wrapper != nil {
			maconn = d.Wrapper(maconn)
		}

		c, err := newSingleConn(ctx, d.LocalPeer, remote, maconn)
		if err != nil {
			maconn.Close()
			errOut = err
			return
		}

		if d.PrivateKey == nil || EncryptConnections == false {
			log.Warning("dialer %s dialing INSECURELY %s at %s!", d, remote, raddr)
			connOut = c
			return
		}

		c2, err := newSecureConn(ctx, d.PrivateKey, c)
		if err != nil {
			errOut = err
			c.Close()
			return
		}

		connOut = c2
	}()

	select {
	case <-ctx.Done():
		logdial["error"] = ctx.Err()
		logdial["dial"] = "failure"
		return nil, ctx.Err()
	case <-done:
		// whew, finished.
	}

	if errOut != nil {
		logdial["error"] = errOut
		logdial["dial"] = "failure"
		return nil, errOut
	}

	logdial["dial"] = "success"
	return connOut, nil
}